Journal of Vibroengineering
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Feature extraction of the weak periodic signal of rolling element bearing’ early fault based on shift invariant sparse coding
Get PDFWhen fault such as pit failure arises in the rolling element bearing the vibration signal of which will take on periodic characteristics, and the abrupt failure of rotating machinery can be avoided effectively if the weak periodic characteristics of the early fault stage is extracted timely. However, the periodic characteristics of bearing’ early weak fault is hard to be extracted usually and the reasons can be boiled to as following: Firstly, the weak periodic signal of rolling element bearing’ early fault stage is buried by the strong background noise. Secondly, the weak fault cannot show the complete shock attenuation impulsive characteristic due to its weak energy, so the traditional wavelet transform would not work effectively if a proper wavelet basis function fitting for analyzing the impulsive characteristics is not selected. To solve the above two problems, a feature extraction method of the weak periodic signal of rolling element bearing’ early fault based on Shift Invariant Sparse Coding (SISC) originating from sparse representation is proposed in the paper. To capture the underlying structure of machinery fault signal, SICS provides an effective basis functions learning scheme by solving the flowing two convex optimization problems iteratively: 1) L1-regularized least squares problem. 2) L2-constrained least squares problem. The fault feature can be probably contained and extracted if optimal latent component is filtered among these basis functions. The feasibility and effectiveness of the proposed method are verified through the corresponding simulation and experiment
A generalised entropy in multifractal time signals analysis of mechanical vibration
Get PDFThe entropy theory finds wider and wider applications in the description of real time series recorded in complex systems. The relation of the multifractal spectrum with the Renyi dimension allows to assess the generalised entropy of time series based on the multifractal formalism. The aim of the hereby paper is to present the form and properties of entropy, which can be used in defining measures in the comparative analysis of mechanical vibrations time series being the main information source on the complex systems states. The obtained results were verified for signals recorded in various maintenance states of the drive system of the spark ignition vehicle, being the effect of active experiment with implemented typical mechanical defects
Influence of shaft torsional stiffness on natural characteristics of four-stage main transmission system in three-engine helicopter
Get PDFFour-stage main helicopter transmission system occupies several strong points like good carrying capacity and is addressed by many scholars. However, the influence of variable parameters on natural characteristics in a three-engine helicopter, is not to be investigated, according to the limited published issues. Thus, in the study, a vibration model of the four-stage main helicopter transmission system is established through the lumped mass method. In the model, many factors, including time-varying meshing stiffness and torsional stiffness of gear shaft are considered. The differential equation of the system is solved via the Fourier method, 27-orders natural frequency and modal shape corresponded by each degree of freedom (DOF) of the system are obtained. The influence of the shaft torsional stiffness on the first five orders of the system natural frequency is studied. Besides, the impact of the matching relationship of key shafts’ torsional stiffness on the system stability is analyzed. These contributions would improve modification developments of four-stage deceleration helicopter in future
Deployment accuracy analysis of cable-strut deployable mechanism with joint clearances and forces constrained
Get PDFThe effects on deployment accuracy of joint clearances and forces acting on the deployable mechanism are investigated. “A virtual massless link” is used to describe the joint clearance of the mechanism in the free state. Aiming at the following problems of multi-loop linkages mechanical system such as loop constraints coupling and complicated topology structure, the geometric relationships and the deploying error equations of deployable mechanism are provided based on Denavit-Hartenberg matrix by splitting multi-loop linkage into 3 single-loop linkages. In addition, with consideration of forces, “a virtual massless rope” is used instead of “virtual massless link” to describe the joint clearance for avoiding the extra singularities. And the criterion of mechanism in stable configuration is obtained by weighting coefficient method on the basis of minimum potential principle. The solving procedure of deploying error equations in the state of forces constrained is presented by combining Monte-Carlo method with genetic algorithm, it is an effective solution for the nonlinear objective function with multiple constraints and strong coupling. The results indicate that the appropriate forces acting on mechanism produce a significant effect on improving repeat accuracy, and the absolute accuracy can be improved with the future error compensation
Free vibration of functionally graded SWNT reinforced aluminum alloy beam
Get PDFAluminum alloy (Al-alloy) reinforced with Single walled carbon nanotubes (SWNT), which represents an important industrial application, is studied. Different beam theories (BT) are applied to investigate functionally graded (FG) beams made of Al-alloy reinforced with randomly oriented, straight and long SWNT. The Rayleigh-Ritz method is used to estimate the beam frequencies. First, the Mori-Tanak (M-T) homogenization technique is used to predict the effective material properties of the beams. Second, results from BT are verified against finite element (FE) simulations. Next, a parametric study is carried out in order to investigate the influence of SWNT volume fractions, SWNT distributions and beam edge-to-thickness ratios on the vibration behavior of the FG beam. Results demonstrate the important effect of the studied parameters on the dynamic behavior of the FG SWNT reinforced Al-alloy composite beams
Dynamic stability of lateral vibration of a tubing string in flowing production
Get PDFTubing string is one of the most important tools in flowing production. In the state of lateral vibration instability of the tubing string, severe collisions between the string and casing may lead to tubing string failure and borehole wall sloughing. Stability of the tubing string is a potential safety hazard in the process of oil and gas production and discussed in this paper. Considering interaction among the gravity, internal fluid hydrodynamic force, reservoir pressure and liquid cushion in the annular, a mechanical model of lateral vibration of the tubing string, which is simplified as a uniform pipe conveying fluid upwards in vertical well, is developed, and the stability of the system is analyzed by the finite element method. The influences of the flow velocity, the bottom hole pressure and the height and density of liquid cushion on the stabilities of tubing string are discussed. It is found that the increase of either the flow velocity or the bottom hole pressure can cause the buckling of tubing string, however, increasing the height or density of liquid cushion is helpful to improve the stability of tubing string
An intelligent fault diagnosis method of rotating machinery using L1-regularized sparse filtering
Get PDFTraditional intelligent fault diagnosis methods take advantage of diagnostic expertise but are labor-intensive and time-consuming. Among various unsupervised feature extraction methods, sparse filtering computes fast and has less hyperparameters. However, the standard sparse filtering has poor generalization ability and the extracted features are not so discriminative by only constraining the sparsity of the feature matrix. Therefore, an improved sparse filtering with L1 regularization (L1SF) is proposed to improve the generalization ability by improving the sparsity of the weight matrix, which can extract more discriminative features. Based on Fourier transformation (FFT), L1SF, softmax regression, a new three-stage intelligent fault diagnosis method of rotating machinery is developed. It first transforms time-domain samples into frequency-domain samples by FFT, then extracts features in L1-regularized sparse filtering and finally identifies the health condition in softmax regression. Meanwhile, we propose employing different activation functions in the optimization of L1SF and feedforward for considering their different requirements of the non-saturating and anti-noise properties. Furthermore, the effectiveness of the proposed method is verified by a bearing dataset and a gearbox dataset respectively. Through comparisons with the standard sparse filtering and L2-regularized sparse filtering, the superiority of the proposed method is verified. Finally, an interpretation of the weight matrix is given and two useful sparse properties of weight matrix are defined, which explain the effectiveness of L1SF
Application of time-frequency method for research on influence of locomotive wheel slip on vibration
Get PDFWheel-rail contact phenomena is problem considered in many scientific manuscripts. Mostly the research is focused on wear, friction and forces analysis. This paper presents research on rail vibration generated due to rail vehicle passage. The problem investigated was the influence of wheel slip phenomena on vibration of rail. The locomotive wheel slip can be caused due to braking, flat wheel or defect (wear) of rail surface. Therefore, results of presented investigations can be useful for many applications, including rail vehicle driving monitoring system, control system, especially due to braking distance or diagnostics of wheels of railway tracks. The research was taken place on experimental test track. For the complex analysis horizontal and vertical vibration were measured. The investigation requires regular train vehicle drive condition, where the wheels are rolling on the rail surface without wheel slip and second case for drive process including wheel rolling and wheel slip (friction rolling and sliding). The vibration signals are non-stationary thus its processing should be conducted simultaneously in the time and frequency domain, as time-frequency representation (TFR). For this purpose, Short Time Fourier Transform (STFT) and Continuous Wavelet Transform (CWT) can be employed
Railway axle box bearing fault identification using LCD-MPE and ELM-AdaBoost
Get PDF. In this study, a new method for bearing fault diagnosis using local characteristic-scale decomposition multi-scale permutation entropy (LCD-MPE) and extreme learning machine AdaBoost (ELM-AdaBoost) algorithms is proposed. Vibration signals of railway axle box rolling bearings under 4 conditions (normal, outer race fault, inner race fault, and rolling element fault) were used as our research objects. The signals were de-noised using wavelet de-noising (WD) as a pre-filter, then the LCD was used to decompose the signal into a number of intrinsic scale components (ISCs). Then, the multi-scale permutation entropy (MPE) was extracted as the feature parameters. Finally, the extracted features were used as ELM-AdaBoost to achieve the automated fault diagnosis. Our results prove that our method is effective for an accurate diagnosis of railway axle box bearing faults. Furthermore, our fault diagnosis method is highly applicable in practical engineering
Damped vibrations of the Γ type frame with open cracks
Get PDFThis paper discusses the formulation and solution for the problem of damped transverse vibrations of the Γ type frame with open cracks. Dissipation of vibration energy in the frame results from the movement constraint in the column and bolt support (constructional damping) and internal damping of viscoelastic material of the frame (rheological model by Kelvin-Voigt). Presence of a crack impacts local flexibility that has an effect on frame vibration response. The boundary problem for the above system was formulated based on the Hamilton’s principle and solved numerically for the complex eigenvalues ω*. The effect of the crack depth and its location on damped vibration was presented. The effect of both types of damping on the degree of amplitude decay was also presented